Sintered hard metal alloy for machining cast iron and steel



United States Patent Office 3,245,763 Patented Apr. 12, 1966 3,245,763 SINTERED HARD METAL ALLOY FOR MACHINING CAST IRON AND STEEL Fall Johan Olof William Ohlsson, Enskede, and Stig Anders Olof Iggstriim, Bandhagen, Sweden, assignors to Sandvikens Jernverks Aktiebolag, Sandviken, Sweden, a corporation of Sweden N Drawing. Filed June 22, 1964, Ser. No. 377,094 Claims priority, application Sweden, July 1, 1963, 7,258/63 12 Claims. (Cl. 29182.7)

The present invention relates to a sintered, fine grained hard metal alloy having excellent properties for machining cast iron and steel. In comparison with previously known sintered hard metal alloys for this purpose the alloy according to the invention has a superior wear resistance in combination with a very high toughness. The alloy has a composition of the known type and contains carbide of tungsten as the main component, together with carbide of titanium and preferably one or more additional carbides such as carbide of tantalum and/or niobium and a bonding metal such as cobalt and/ or nickel. It has been found to be a necessary condition for the alloy according to the invention that it contains by volume 60- 80% of WC, -25% of TiC, 020% of TaC, NbC and/or VC, 010% of Cr C ZrC and/or HfC, 05% of Mo and/or carbide of molybdenum, the remainder being in the main Co and/or Ni and possibly also Fe. The total quantity of Co, Ni and Fe should not exceed 9.5% and the content of Fe should not exceed 6% by volume.

The following all percentages are by volume unless otherwise stated.

It is of decisive importance that the alloy has a certain structure with regard to the phases of the alloy and the grain size of the carbides in order to obtain the unexpected improvement of the properties which is characteristic for the alloy according to the invention. The mean (average) grain size of the carbide grains should thus be smaller than 1.6 microns (,u), preferably smaller than 1.5 microns, and at the same time the alloy should be manufactured in such a way that it contains 37.5i7.5% of 'y-phase, 8.5i1% of ,B-phase (bonding metal), the remainder consisting in the main a-phase. Insignificantly amounts of one or more additional phases as -phase can possibly also be present. A characteristic property of the alloy according to the invention is that it has a very fine grained structure in relation to the above said phase distribution.

The 'y-phase is composed of one or more cubic carbides such as TiC, TaC, NbC, VC, ZrC and HfC and which in solid solution contains a not too insignificant amount of WC. The fi-phase is a bonding metal phase containing for instance Co, while the OL-PhaSC consists of pure WC, possibly containing a small amount of M0 in solid solution. In addition minor quantities of other phases, for instance a phase consisting of Mo C may be present.

Particularly good results have been obtained when the -phase is 40i5%. It has been found that the fl-phase should have a face centered cubic and/ or hexagonal close packed crystal lattice. For this purpose the bonding metal should suitably contain a major portion of Co and/or Ni. The bonding metal can also contain Fe, the Co and/or Ni being partially substituted by Fe, preferably at the most to such an extent that the bonding metal phase does not lose its above mentioned face centered cubic and/ or hexagonal close packed lattice.

For persons skilled in the art there are no Special difliculties in obtaining the above mentioned narrow phase ranges in manufacturing the alloy, the characteristic features of the alloy and its structure being defined and being in a well known manner dependant upon the sintering temperature, the time period for sintering and the properties of the initial materials. The process of manufacture therefore forms no part of the present invention.

Besides the said relation between the phases the alloy should as mentioned have a grain structure which is unusually fine grained With regard to the said phase relation. This is of great importance for obtaining the desired valuable properties in connection with the cutting ability of the alloy for use in machining. For this purpose the grain size should lie Within such a range that the coercive force, which is easily measurable, is not less than 200 and preferably not less than 220 oersted, at least when the bonding phase comprises in the main Co. As a rule the grain size should have such a value that the coercive force is 230-330 oersted.

It is generally known that the coercive force is related to the grain size of the carbide grains in a sintered hard metal in such a way that a diminishing of the grain size results in an increase of the coercive force and vice versa. It is therefore possible to use the coercive force in defining the grain size. There are certain deviations from this general rule. A large quantity of Fe in the bonding metal phase lowers the coercive force and some complex carbides as n-phase raises the coercive force. Ni also can give deviations from the said rule.

The alloy according to the invention will have the same superior qualities even if Co is wholly or partly substituted by Ni, or if Co and/or Ni are partly substituted by Fe. This substitution should as mentioned be performed only to such an extent that the fi-phase maintains its face centered cubic and/or hexagonal close packed lattice. Further the grain size should correspond to the grain size of an alloy with Co alone or with Co and up to 0.5% each of Ni and Fe as a bonding metal, the composition and phase structure being in other respects the same, the latter alloy having such a grain size that the coercive force is at least 200 and preferably at least 220 oersted. The estimation of the grain size in such alloys in which Co has been wholly or partly substituted, can be made by comparing the structures of said alloys in a light or electron microscope with the structure of an alloy containing Co or C0 and at the most 0.5% each of Ni and Fe in the bonding metal phase.

In order to obtain the desired qualities with regard to the wear strength and toughness the alloy according to the invention should be unusually fine grained in view of the relatively high content of 'y-phase. Thus the mean grain size of the carbide grains should lie below 1.6 microns and preferably below 1.5 microns. As a lower limit can be mentioned 0.5 micron. Normally the mean grain size should lie within the range 0.7-1.4 microns. For certain very tough qualities the range 0.8-1.2 microns has been found especially suitable.

The stoichiometric composition of the alloy is of course also important for obtaining the desired qualities. Said composition should be chosen within the above-mentioned limits. Thus the content of WC should lie within the range 60-80%. As a rule the narrower range 65-75% has been found especially suitable. The alloy should also contain 1025 and preferably 15-25 of TiC. The alloy can further contain up to 20% of TaC, NbC and/ or VC. If it contains only TaC and/or NbC the content of these alloy elements should normally not exceed 15%. Preferably the alloy contains a relatively small quantity, 0.5-10% TaC and/or NbC. In addition the alloy can contain up to 10% of Cr C ZrC and/or HfC and up to 5% M0. The M0 changes at least partly to carbide as Mo C and MoC during the sintering of the alloy. In this connection it can be mentioned that some Mo can form a solid solution in the a-phase, which consists of WC. The content of Co and/or Ni should at the most be 9.5%. They can, as mentioned, be partly substituted by 3 Fe but only to such an extent that the bonding metal phase does not lose its face centered cubic and/or hexagonal close packed lattice. The Fe-content should at the most be 6% and the total content of Co and/or Ni and Fe 9.5%. Usually the content of Fe is at the most 1 or 0.5%. The content of bonding metal, which wholly or to a major part consists of Co and/or Ni with or without a certain amount of Fe, should be at least 7.5 and at the most 9.5%. The range 89% has been found especially suitable.

In order to obtain the above mentioned surprising improvement of the ability to cut cast iron and steel it is necessary that the alloy has the above defined composition. The structure of the alloy with regard to the phase composition and the grain size is of decisive importance, and it is also necessary that the earlier defined conditions in this respect are at the same time fulfilled.

The following are examples of compositions and the phase relations in said compositions of two alloys according to the invention:

TiC "percent" -0. 22 (Ta, Nb)C do 1. C0 8.5 9 WC 70.0 09 Mean gram s microns. 1. 3 1. 2 Coercive force Hoersted 2-0 260 -phase "percent. 41. 0 44 B-phase... 1 a do. 8.5 9 a-phase do 50. 5 47 In the following are given some comparative examples of working tests with an alloy according to the invention and other alloys which are regarded as being suitable for the actual purpose. In the following table column A relates to the alloy according to the invention and columns B-G relate to the alloys of comparison. The alloys B, C, D and F are examples of alloys which are normally used for machining cast iron while the alloy E is intended for so called universal machining, that is, machining both cast iron and steel, and the alloy G is intended for machining of steel. The alloy contents and the phase quantities are given in percents of volume. It can be pointed out that the alloys C and F are fine grained but have a content of 'y-phase which is only 4 and 2% respectively.

Alloys Data A B C D E F G Coercive force, oersted.. 240 190 290 180 150 270 125 'y-pllase 41. 0 7. 0 4. 0 4. 5 24. 0 2. 0 50. 0 b-phase 8. 5 9. 0 6. 5 10. 0 8. 5 10. 5 13. 0 a-phase 50. 5 84. 0 89. 5 85. 5 67. 5 87. 5 37. 0 Mean grain size, microns. 1.3 1. 9 1. 4 1. 8 2. 7 1.0 2. 2

The above mentioned sintered hard metal alloys have been practically tested and compared. The following report of said tests comprises Examples l-3 referring to machining of cast iron and Example 4 referring to machining of steel. The wear resistance of the alloys has been determined by measuring the wear of the side surface and the top surface of the cutting insert, i.e. the flank wear and the cratering. The examples clearly illustrate that the wear resistance of the alloy according to the invention is superior in comparison with the other alloys tested.

Example 1 Material Grey perlitic cast iron HB 220 (Brinell hardness). Work piece Brake drum. Operation Rough turning (roughing Cutting speed 93 meters/minute. Feed 0.32 mm./turn.

Cutting depth 2 mm. Feed length 35 mm./piece.

Alloy quality A B C Number of pieces 20 2O 20 Flank, wear, mm." 0.31 0. 50 0. 43 Cratering, microns 54 131 170 Example 2 Material Cast iron 66 26 (according to DIN 1691, German standard). Work piece Hub. Operation Internal turning, rough.

surface. Cutting speed 148 meters/minute. Feed 0.2 mm./turn. Cutting depth 35 mm. Feed length 40 mm./piece.

Alloy quality A B D Number of pieces 18 18 18 Flank, wear, mm-" 0.31 1. 34 1. 66 Cratering, microns 111 185 213 Example 3 Material Cast iron SIS 0115 (Swedish standard). Work piece Tube (1 200 mm. Operation External turning. Feed 0.25 mm./turn. Cutting depth 1.5 mm. Feed length 200 mm.

Alloy quality A B F Cutting speed, meters/minute 220 220 220 Flank, wear, mm 0. 42 0.62 0.73 Cratering, microns 20 25 28 Cutting speed, meters/minute 240 240 240 Flank, wear, mm 0. 51 0.77 0.81 Cratering, microns 25 34 38 Example 4 Material Carbon steel 1% C, HB 280 (Brinell hardness). Work piece Shaft mm. Operation External turning. Cutting speed m./min. Feed 0.45 mm./ turn. Cutting depth 1.5 mm. Feed length 750 mm.

Alloy quality H, A E i G Flank wear, mm 0.25 0.37 0.32 Cratering, microns 70 95 We claim:

1. Sintered fine grained hard metal alloy adapted for machining cast iron and steel and containing by volume 60-80% of WC, 1025% of TiC, 020% of at least one member selected from the group consisting of T aC, NbC and VC, 010% of at least one member selected from the group consisting of Cr C ZrC and HfC, 05% of at least one member selected from the group consisting of Mo and carbide of molybdenum, the remainder consisting essentially of at least one member selected from the group consisting of Co, Ni and Fe, the total amount of Co, Ni and Fe being at the most 9.5%, the amount of Fe being at the most 6%, the mean grain size of the carbide grains being less than 1.6 microns, the alloy containing 37.5i7.5% of y-phase, 8.5:1% of B-phase and the remainder being in the main a-phase.

2. Sintered hard metal alloy according to claim I, having a coercive force exceeding 200 oersted.

3. Sintered hard metal alloy according to claim 1 in which the B-phase has a face centered cubic lattice.

4. Sintered hard metal alloy according to claim 1 in which said ,B-phase consists of at least one member selected from the group consisting of Co, Ni and Fe.

5. Sintered hard metal alloy according to claim 1 in which said 'y-phase amounts to 40.0i5.0%.

6. Sintered hard metal alloy according to claim 1 in which the mean grain size of the carbide grains is greater than 0.5 micron.

7. Sintered hard metal alloy according to claim 1, characterized in that it contains 0-15 of at least one member selected from the group consisting of TaC and NbC.

8. Sintered hard metal alloy according to claim 1 in which it contains 15-25% of TiC.

9. Sintered hard metal alloy according to claim 1 in which it contains 7.59.5% of said B-phase.

10. Sintered hard metal alloy according to claim 1 in which it contains not more than 1.0% of Fe.

11. Sintered hard metal alloy according to claim 1 in which it contains 65-75% of WC.

12. Sintered fine grained hard metal alloy adopted for machining cast iron and steel and containing by volume 65-75% of WC, -25% of TiC, 0.5-10% of at least one member selected from the group consisting of T210 and 6 NbC, 0-10% of at least one member selected from the group consisting of Cr C ZrC and HfC, O-5% of at least one member selected from the group consisting of Mo and carbide of molybdenum, the remainder consisting essentially of at least one member selected from the group consisting of Co, Ni and Fe, the total amount of Co, Ni and Fe being 7.5-9.5 the amount of Fe being at the most 1.0%, the mean grain size of the carbide being less than 1.6 microns, the alloy containing 1,973,428 9/1934 Comstock 29-182.7 2,169,090 8/1939 Dawihl et al 29-182] 2,188,983 2/1940 Padowicz 29l82.7 2,899,739 8/1959 Ohlsson 29182.7

FOREIGN PATENTS 763,409 12/1956 Great Britain.

LEON D. ROSDOL, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner. 

1. SINTERED FINE GRAINED HARD METAL ALLOY ADAPTED FOR MACHINING CAST IRON AND STEEL AND CONTAINING BY VOLUME 60-80% OF WC, 10-25% OF TIC, 0-20% OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF TAC, NBC AND VC, 0-10% OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF CR2C3, ZRC AND HFC, 0-5% OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF MO AND CARBIDE OF MOLYBDENUM, THE REMAINDER CONSISTING ESSENTIALLY OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF CO, NI AND FE, THE TOTAL AMOUNT OF CO, NI AND FE BEING AT THE MOST 9.5%, THE AMOUNT OF FE BEING AT THE MOST 6%, THE MEAN GRAIN SIZE OF THE CARBIDE GRAINS BEING LESS THAN 1.6 MICRONS, THE ALLOY CONTAINING 375.5$7.5% OF Y-PHASE, 8.5$1% OF B-PHASE AND THE REMAINDER BEING IN THE MAIN A-PHASE. 